CABLE TRENCH EXCAVATION FOR POWER CABLE: UNDERGROUND PROJECT

Trenches Excavation  and Underground Cable Installation

The exact location of each trench should be selected and approved by the Engineer before cable trench excavation for the power cable of any underground cable project.

Trenches should be kept as straight as possible and each trench shall be excavated to an approved formation and dimensions and shall have vertical sides which would be timbered where necessary so as to avoid subsidence and damage.

It’s important to  excavate up to a depth of at least 100 mm below the base of cable laying. The bottom of each trench should be firm and of smooth contour. 

Where trenches pass from a footway to a roadway or at other positions where a change of level is necessary, the bottom of the trench shall rise or fall gradually. The minimum width shall be at least 600 mm for a single cable. 

For multiple cables, the trench width would be determined from the minimum separation specified and the diameter of cables and approved by the qualified Engineer.

The servicer should take reasonable precautions to prevent damage to the highway or ground surface from a slip or breaking away of the sides of the trench. The rate of rise or fall should be taken into consideration.

It should be dealt with and disposed of water so as to prevent any risk of the cables and other materials to be laid in the trenches being affected detrimentally. Necessary to provide facility for all pumps and appliances required and should carry out the necessary pumping and bailing.

It needs to consider the provision be made during excavation for reasonable access of persons and vehicles to property or places adjacent to the route. This provision shall be maintained until restoration has been completed.

Before each excavation is commenced the contractor shall make a written or documented application to the Engineer prior to starting work attaching with the application a dimensioned sketch detailing and positioning the proposed excavation. 

No work may be commenced until the appropriate authority has issued a “Permit to Excavate” in accordance with the Letter of Application.

When the excavation for trenches has been accurately executed, notice shall be given by the contractor to the authority Engineer, Laying of cables or building of structures will not be started until the contractor has obtained the authority Engineer’s sanction to proceed with the work.

After any cable has been laid and until the whole of the cables to be laid in the trench have been covered with their protective covers shall be used in the trench or placed in such a position that they may fall into the trench. 

Rollers must be used during the laying of cables, and ensure there are no sharp projecting parts liable to damage the cables.

After complete backfilling, it would be clear and level the works so that the finished reinstated ground level shall be the same as that which pertained prior to the commencement of the works.

Cable Damages During Excavation & Installation

The servicer must take all reasonability and precautions to avoid any damage to buried services, existing surface and other encumbrances land, property, roads, fences, walls, gates any kind of public or private property or environmental issues, and must ensure that the work is adequately supervised so that unavoidable damage is reduced to the minimum. 

The work servicer will be liable for all damage arising by or in consequence of the works and should pay compensation. After completing the installation job, of course, remove all spoil and surplus material from sites.

Consider the following facts that often damage the cable during excavation and installation:

1. Consider existing underground power lines, communication lines, gas lines, water lines, and many more utility services hidden underground;
2. Consider any metallic or sharp object that may be hidden in any place;
3. Handle and shift the cable drum carefully to avoid cable damage;
4. Use the proper jack to lift the cable drum;
5. Use a sufficient roller to pull the cable, a special bend roller must used in a curved trench;
6. Remove stone, chips, or any foreign materials from the trench before cable pulling, and cover up with sand as soon as cable pulling is completed;
7. Don’t apply too much tension to pull the cable;
8. Take special care at the road crossing point during cable pulling;
9. Don’t ignore any suspicious or theft possibility.

Thrust Boring, Heading, and Tunnels for Cable Trenches

It’s often to face road crossing, rail line crossing, drains, and canal crossing during trench excavation for power cable installation. These crossings should follow some special rules and conditions as per international and local codes.

Work on thrust boring headings or tunnels shall be carried out as an adequate instruction. It should take all reasonable steps to ascertain the position of all sewers, drains, pipes, and structures and these must be recorded on a drawing showing the cross-section and levels or the proposed works before operations commence.

Thrust boring is just a blind job, so must be ensured there are no utility services or not affected during carry out this job. Especially cable crossing a rail line, thrust boring is necessary.

 

Obstructions for Cable Trenches Excavation

When in the course of the contractor works obstructions are encountered which necessitate diversions of or alteration to other underground works or alterations to buildings or foundations or when conditions necessitate the adoption of a special form of the trench the contractor shall immediately notify the authority engineer further work shall not proceed until written instruction has been obtained from the authority.

Excavated Materials for Cable Trenches

The material excavated from each trench shall be placed so as to prevent nuisance or damage. 

Where this is not possible, the excavated material shall be removed from the site and returned for refilling the trench upon completion of laying. Surplus material shall be disposed of in an adequate way that will not be harmful.

Disposing of any level of hazardous materials should follow the local or international hazard disposal rules.

Cable and Joints Route Marker

Cable markers of an approved type shall be provided along the route of buried cables as required to reinstatement is being carried out. Markers shall be installed vertically over each cable at a maximum of 50m intervals or any requirement at all road crossings and joint positions.

Cable route and joint marking can reduce the operation and maintenance time during any fault occur, as well as help to future plan for other utility company visible the existing cable route.

Protective Cover for Cables

To protect the installed cable from any damages, protective covers shall be made of RC slabs each 75 mm thick, 300 mm wide, and length as required or any special measurement and protecting materials.

Warning also be put along the trench over the protective slab that will ensure warning, there are power cables just below.